The following abbreviations and terms are herewith defined, at least some of which are referred to within the following description of the present disclosure.
3GPP 3rd-Generation Partnership Project
AGCH Access Grant Channel
ASIC Application Specific Integrated Circuit
BLER Block Error Rate
BSS Base Station Subsystem
CC Coverage Class
CN Core Network
DRX Discontinuous Receive Cycle
EC-GSM Extended Coverage Global System for Mobile Communications
EC-PCH Extended Coverage Paging Channel
eDRX Extended Discontinuous Receive
eNB Evolved Node B
DL Downlink
DSP Digital Signal Processor
EDGE Enhanced Data rates for GSM Evolution
EGPRS Enhanced General Packet Radio Service
FN Frame Number
GSM Global System for Mobile Communications
GERAN GSM/EDGE Radio Access Network
GPRS General Packet Radio Service
GPS Global Positioning System
HARQ Hybrid Automatic Repeat Request
IMSI International Mobile Subscriber Identity
IoT Internet of Things
LTE Long-Term Evolution
MCS Modulation and Coding Scheme
MF Multiframe
MFRM Multiframe
MFRMS Multiframes
MME Mobility Management Entity
MS Mobile Station
MTC Machine Type Communications
NB Node B
N-PDU Network Protocol Data Unit
PCH Paging Channel
PDN Packet Data Network
PDTCH Packet Data Traffic Channel
PDU Protocol Data Unit
PS Packet Switched
RACH Random Access Channel
RAN Radio Access Network
RAT Radio Access Technology
RAU Routing Area Update
SGSN Serving GPRS Support Node
TDMA Time Division Multiple Access
TS Technical Specification
UE User Equipment
WCDMA Wideband Code Division Multiple Access
WiMAX Worldwide Interoperability for Microwave Access
Coverage Class (CC): At any point in time a wireless device belongs to a specific uplink/downlink coverage class that corresponds to either the legacy radio interface performance attributes that serve as the reference coverage for legacy cell planning (e.g., a Block Error Rate of 10% after a single radio block transmission on the PDTCH) or a range of radio interface performance attributes degraded compared to the reference coverage (e.g., up to 20 dB lower performance than that of the reference coverage). Coverage class determines the total number of blind transmissions to be used when transmitting/receiving radio blocks. An uplink/downlink coverage class applicable at any point in time can differ between different logical channels. Upon initiating a system access a wireless device determines the uplink/downlink coverage class applicable to the RACH/AGCH based on estimating the number of blind transmissions of a radio block needed by the BSS (radio access network node) receiver/wireless device receiver to experience a BLER (block error rate) of approximately 10%. The BSS determines the uplink/downlink coverage class to be used by a wireless device on the assigned packet channel resources based on estimating the number of blind transmissions of a radio block needed to satisfy a target BLER and considering the number of HARQ retransmissions (of a radio block) that will, on average, be needed for successful reception of a radio block using that target BLER. Note: a wireless device operating with radio interface performance attributes corresponding to the reference coverage (normal coverage) is considered to be in the best coverage class (i.e., coverage class 1) and therefore does not make any additional blind transmissions subsequent to an initial blind transmission. In this case, the wireless device may be referred to as a normal coverage wireless device. In contrast, a wireless device operating with radio interface performance attributes corresponding to an extended coverage (i.e., coverage class greater than 1) makes multiple blind transmissions. In this case, the wireless device may be referred to as an extended coverage wireless device. Multiple blind transmissions corresponds to the case where N instances of a radio block are transmitted consecutively using the applicable radio resources (e.g., the paging channel) without any attempt by the transmitting end to determine if the receiving end is able to successfully recover the radio block prior to all N transmissions. The transmitting end does this in attempt to help the receiving end realize a target BLER performance (e.g., target BLER≤10% for the paging channel).eDRX cycle: eDiscontinuous reception (eDRX) is a process of a wireless device disabling its ability to receive when it does not expect to receive incoming messages and enabling its ability to receive during a period of reachability when it anticipates the possibility of message reception. For eDRX to operate, the network coordinates with the wireless device regarding when instances of reachability are to occur. The wireless device will therefore wake up and enable message reception only during pre-scheduled periods of reachability. This process reduces the power consumption which extends the battery life of the wireless device and is sometimes called (deep) sleep mode.Extended Coverage: The general principle of extended coverage is that of using blind transmissions for the control channels and for the data channels to realize a target block error rate performance (BLER) for the channel of interest. In addition, for the data channels the use of blind transmissions assuming MCS-1 (i.e., the lowest modulation and coding scheme (MCS) supported in EGPRS today) is combined with HARQ retransmissions to realize the needed level of data transmission performance. Support for extended coverage is realized by defining different coverage classes. A different number of blind transmissions are associated with each of the coverage classes wherein extended coverage is associated with coverage classes for which multiple blind transmissions are needed (i.e., a single blind transmission is considered as the reference coverage). The number of total blind transmissions for a given coverage class can differ between different logical channels.MTC device: A MTC device is a type of device where support for human interaction with the device is typically not required and data transmissions from or to the device are expected to be rather short (e.g., a maximum of a few hundred octets). MTC devices supporting a minimum functionality can be expected to only operate using normal cell contours and as such do not support the concept of extended coverage whereas MTC devices with enhanced capabilities may support extended coverage.Nominal Paging Group: The specific set of EC-PCH blocks a device monitors once per eDRX cycle. The device determines this specific set of EC-PCH blocks using an algorithm that takes into account its IMSI, its eDRX cycle length and its downlink coverage class.
In the GSM/EDGE Radio Access Network (GERAN), a feature called extended discontinuous reception (eDRX) has been introduced. The eDRX feature extends the maximum legacy paging cycle of 2.12 seconds up to about 52 minutes and thereby allows wireless devices to still be reachable while at the same time saving the battery consumption of the wireless devices by allowing longer durations of sleep between reachability events. From a network perspective, when the eDRX feature is supported, it will need to be supported in all cells within a Routing Area thereby allowing the network to identify the point in time within an eDRX cycle that a given wireless device becomes reachable using its nominal paging group. This point in time when a wireless device is reachable will be the same regardless of the actual cell it is camped on. From a wireless device perspective, the wireless device will need to be able to determine this same point in time so it can wake up and read the same nominal paging group on the paging channel. The wireless device may need to take time drift as well as a possible change of location into account when determining how early it should wake up prior to its nominal paging group.
In order to reach a wireless device supporting eDRX, a Base Station Subsystem (BSS) (radio access network node) needs to transmit the page using the appropriate paging group, but with limited buffering capacity, the page request from the Serving GPRS Support Node (SGSN) (core network node) needs to be sent to the BSS shortly before the next occurrence of the wireless device's nominal paging group in order for the page request to avoid being discarded due to insufficient buffer capacity. In other words, when downlink data for a wireless device arrives at the SGSN, the SGSN needs to determine when the next instance of the nominal paging group for that particular wireless device occurs on the radio interface in order to be able to calculate the appropriate time to transmit the page request to the BSS.
There are currently two different techniques for the SGSN to determine when the nominal paging groups for wireless devices occur on the radio interface. In the first technique, the SGSN transmits a PAGING-PS Protocol Data Unit (PDU) to the BSS when downlink data arrives at the SGSN. If the BSS determines that the nominal paging group of the wireless device occurs too far into the future (e.g., the BSS is unable to buffer the paging request until the next occurrence of the nominal paging group for the indicated wireless device), the BSS responds to the PAGING-PS PDU by transmitting a PAGING-PS-REJECT PDU to the SGSN and includes therein information indicating the time until the next paging occasion (i.e., when the next instance of the nominal paging group for the wireless device occurs). This technique is disclosed in section 7.1 of 3GPP TS 48.018 V13.0.0 (December 2015) entitled “Base Station System (BSS)—Serving GPRS Support Node (SGSN); BSS GPRS Protocol (BSSGP)(Release 13)”. The entire contents of this document are hereby incorporated by reference herein for all purposes.
In the second technique, the SGSN may transmit to the BSS a DUMMY-PAGING-PS PDU at any time to determine the time until the next paging occasion for the wireless device indicated therein. The BSS uses the information provided within the DUMMY-PAGING-PS PDU to calculate the time until the next paging occasion for the indicated wireless device and includes it within a DUMMY-PAGING-PS-RESPONSE PDU that the BSS transmits back to the SGSN. This method is mainly to be used when a BSS restart indication is received at the SGSN in order to allow the SGSN to adjust timing information for all wireless devices that use extended DRX. This technique is disclosed in the following: (1) the co-assigned U.S. application Ser. No. 15/154,708 entitled “Core Network Node and Method—Time Coordinated Cells for Extended Discontinuous Receive (eDRX)”; and (2) the co-assigned U.S. application Ser. No. 15/154,724 entitled “Radio Access Network Node and Method—Time Coordinated Cells for Extended Discontinuous Receive (eDRX)”. The entire contents of each of these documents are hereby incorporated by reference herein for all purposes.
In the two existing techniques, for every instance of downlink data (e.g., an N-PDU) arriving at the SGSN for a given wireless device, the SGSN needs to transmit a corresponding PAGING-PS PDU or DUMMY-PAGING-PS PDU to the BSS, and the BSS needs to calculate the time until the next paging occasion for the indicated wireless device and return that information in the PAGING-PS-REJECT PDU or DUMMY-PAGING-PS-RESPONSE PDU to the SGSN, unless the paging request can be buffered in the BSS in the case for the PAGING-PS PDU. A problem with these two existing techniques is that the SGSN needs to perform these procedures every time the SGSN receives an instance of downlink data (e.g., N-PDU) for every individual wireless device, which can lead to a high signaling load across the Gb interface between the BSS and the SGSN. This problem is addressed by the present disclosure.